In recent years, the research on organic semiconductor is exceptionally active. The performance of the organic FET is superior to that of the amorphous silicon thin film transistor (a-Si:H TFT). In particular, the mobility of some organic micro-molecule oligomers (e.g. Pentacene, Tetracene, etc.) is over 1 (square centimeter per volt per second) at room temperature. So, the organic FET is potential in such practical applications as flexural integrated circuit (to be abbreviated as IC hereinafter), active matrix display and so on.
The organic FET generally adopts the bottom electrode configuration or the top electrode configuration. WO99/40631 disclosed a device with a vertical geometrical configuration. FIG. 1 shows the existing three geometrical configurations which were applied to obtain the organic FET, wherein, 1 represents the substrate, 2 represents the gate electrode, 3 represents the insulation layer, 4 represents the active layer and 5 represents the source and drain electrodes.
The devices having a bottom electrode configuration and a vertical configurations, respectively, have the advantage of easy to be integrated and processed. But it is difficult to make the later produced organic semiconductor contact with the source and drain electrodes effectively, so that the performance of the devices having two above configurations is inferior to that of the device having a top electrode configuration. Because the organic semiconductor materials are sensitive to some chemical solvents generally used in the processing of the inorganic semiconductor devices, there is difficulty in processing the device having a top electrode configuration by the conventional process for processing inorganic semiconductor devices.
The active layer of the existing organic FET is made of the material with the same molecule. U.S. Pat. No. 5,629,530 disclosed an organic FET having an active layer made of the molecules of the electron donor and receptor together. Because this kind of the semiconductor applies the principle of intermingling P with N to conduct electricity, the performances of switching current ratio and mobility of the FET device with this semiconductor are very poor.